This invention relates generally to the art of welding, and more particularly to a system having an improved back-up pad apparatus for use in welding together the ends of pipes.
The construction of a pipeline involves the joinder of numerous lengths of pipe. Each successive length of pipe is positioned end to end with respect to the preceding length of pipe. The ends of the pipes are then secured by welding. In such welding operations, a strip of material known as a back-up pad is typically applied to the surfaces of the pipes to be joined. The pad faces the line of the weld on the side opposite to that from which the welding operation is to be performed. The use of a back-up pad supports the molten weld material during the weld operation. Formation of irregularities at the joints which could interfere with fluid flow through the pipeline is prevented in this manner. More importantly, the use of a back-up pad results in a more structurally reliable weld. It will be appreciated that back-up pads must be constructed of a durable material to withstand the elevated temperatures which accompany a welding operation.
The prior art contains numerous examples of back-up pads for use in a welding operation. The prior art approaches include utilization of various materials in conjunction with differing designs. For example, back-up pads formed of copper material have been used. One problem involved in using copper back-up pads is that melted copper can become mingled with the welding material or the molten pipe metal, resulting in a weak weld and possible failure of the joint. Another problem is the relatively short useful life of copper back-up pads. Other materials have also been utilized for back-up pads but suffer from similar disadvantages. Heretofore there has not been available a back-up pad capable of extended useage in providing strong uniform welds. There is thus a need for an improved back-up pad apparatus for use in the construction of a pipeline wherein each weld joint is critical.
The present invention comprises an improved back-up pad apparatus which overcomes the foregoing problems and other difficulties associated with the prior art. In accordance with the broader aspects of the invention, there is provided a back-up pad apparatus exhibiting improved performance characteristics over the teaching of the prior art. Each arcuate back-up pad is formed of a hard anodized aluminum material and is capable of multiple useage. Use of the back-up pad of the present invention results in strong and reliable welds between each length of pipe in a pipeline.
According to more specific aspects of the invention, an improved back-up pad apparatus comprises a plurality of arcuate back-up pads mounted on supporting shoes. A groove is provided in the periphery of each back-up pad. The back-up pads include rounded ends and are formed of hard anodized aluminum. Each back-up pad is centrally supported by a support shoe for biased engagement against the interior cylindrical surfaces of two lengths of pipe to be welded. In one embodiment of the invention, cylindrically surfaced members carried by intermediate support shoes are provided between the rounded ends of adjacent back-up pads. The support shoes are slidably mounted on the actuator rods of pipe clamping shoes for radial movement therewith. In another embodient, each back-up pad is pivotally mounted on one support shoe and biased about an axis substantially parallel with the centerline of the pipe.